Classification of bacteria Mrs. Dalia Kamal Eldien MSC in Microbiology Mrs. Dalia Kamal Eldien MSC in Microbiology Lecture NO: 3

Questions for revision the previous lecture  What are the function of bacterial cell wall?  The movement organ in bacterial cell is ……  Define the germination process in bacteria?  What are the function of bacterial cell wall?  The movement organ in bacterial cell is ……  Define the germination process in bacteria?

Objectives At the end of this lecture, the student should know:-  The types of bacteria classified depending on different methods  Emphasis on morphological& staining classification

Introduction  Based on the difference in cellular organization and biochemistry, the kingdom protista has been divided into two groups namely prokaryotes and eukaryotes.  Bacteria and blue-green algae are prokaryotes, while fungi, other algae, fungi and parasite are eukaryotes.  Bacteria are prokaryotic microorganisms that do not contain chlorophyll.  They are unicellular and do not show true branching, except in higher bacteria like actinomycetales.

Classification  The bacteria are classified depending on different methods, include:-  Morphology  Staining reactions  Growth Requirements(Cultural characteristics)  Biochemical reactions  Antigenic structure  Increasingly by their genetic composition using specialized molecular biology techniques. Mrs.:Dalia Kamal Eldien MSC in microbiology

Morphological Classification of bacteria Bacteria are classified according to morphology in to:-  Cocci: are spherical or oval cells  Bacilli: rod shaped cells  Cocobacilli  Vibrios: comma shaped curved rods  Spiral: rigid spiral forms  Spirochetes: flexuous spiral forms Mrs.:Dalia Kamal Eldien MSC in microbiology

Basic shapes of bacteria  Cocci (Singular: coccus) are spherical or oval cells  Bacteria sometime show characteristic cellular arrangement or grouping Mrs.:Dalia Kamal Eldien MSC in microbiology

 According to the plane of cellular division, cocci may be arranged in  Pairs (diplococci)  Chains (streptococci)  Grape like clusters (staphylococci).  Groups of four (tetrads) or eight (sarcina) Mrs.:Dalia Kamal Eldien MSC in microbiology

Cocci in pairs

Cocci in cluster

Cocci in chain

Cocci in tetra

Cocci in sarcina

Basic shapes of bacteria  Bacillus (Singular: bacillus) stick-like bacteria, also name rod shaped  Bacilli are arrange in fewer groups, or singly, or in short chain Mrs.:Dalia Kamal Eldien MSC in microbiology

Bacilli arrangement

Bacilli in chain

Bacilli in single

Vibrios  Vibrios (Singular: vibrio) are small slightly curved rods, comma shape Mrs.:Dalia Kamal Eldien MSC in microbiology

Vibrio (Helicobacter pylori)

Spiral  Spiral (Singular: spirillum) are small, regularly coiled, rigid organisms Mrs.:Dalia Kamal Eldien MSC in microbiology

Spiral bacteria

Spirochetes  Spirochetes (Singular: spirochaete) have a helical shape and flexible bodies Mrs.:Dalia Kamal Eldien MSC in microbiology

Spirochetes

Identify the following bacteria structure?

Bacterial Classification Staining reaction  Classification according to staining reactions depend in different type of stains  The main stain is Gram stain  The Gram staining method is named after the Danish bacteriologist Hans Christian Gram (1853 – 1938) who originally devised it in 1882 (but published in 1884), to discriminate between pneumococci and Klebsiella pneumoniae bacteria in lung tissue Mrs.:Dalia Kamal Eldien MSC in microbiology

Principle of Gram stain  The procedure is based on the ability of microorganisms to retain color of the stains used during the gram stain reaction.  Gram-negative bacteria are decolorized by the alcohol, losing the color of the primary stain, purple.  Gram-positive bacteria are not decolorized by alcohol and will remain as purple.  After decolorization step, a counter stain is used to impart a pink color to the decolorized gram-negative organisms.

Gram stain  Gram staining consists of four components:  Primary stain (Crystal violet, methyl violet or Gentian violet)  Mordant (Gram's Iodine)  Decolourizer (ethyl alcohol, acetone or 1:1 ethanol-acetone)  Counter stain (safranin or neutral red, dilute carbol fuchsin)

Technique of Gram stain  Flood the slide with crystal violet solution for one minute. Wash off briefly with tap water  Flood slide with Gram's Iodine solution, and allow to act (as a mordant) for about one minute. Wash off with tap water.  Flood slide with 95% alcohol for 10 seconds and wash off with tap water. It is most important step  Flood slide with safranin solution and allow to counterstain for 30 seconds. Wash off with tap water  All slides of bacteria must be examined under the oil immersion lens of light microscope

Set of Gram stain

Results of Gram stain  The results of Gram stain will depend on the cell wall  Gram-positive bacteria have a thick mesh-like cell wall which is made up of peptidoglycan (50-90% of cell wall), so it stains as violet.  Gram-negative bacteria have a thinner layer of peptidoglycan (10% of the cell wall) and lose the crystal violet-iodine complex during decolorization with the alcohol rinse, but retain the counter stain Safranin, so it stains as red

Cell wall of Gram positive& negative bacteria

Classification of bacteria according to Gram stain  According to Gram stain, bacteria classify into large groups:-  Gram-positive bacteria (violet color)  Gram-negative bacteria (red color)

Gram-positive bacteria

Gram-negative bacteria

Identify ???